TWI387584B - Process for the production of alkylene carbonate and use of alkylene carbonate thus produced in the manufacture of an alkane diol and a dialkyl carbonate - Google Patents

Description

Process for producing alkyl carbonate and use thereof for alkyl azide esters in the manufacture of alkanediols and dialkyl carbonates

The present invention relates to a process for the production of alkylene carbonate and the use of alkyl carbonates produced thereby for the manufacture of alkanediols and dialkyl carbonates.

A method for producing alkyl carbonate is known. WO-A 2005/003113 discloses a process for contacting carbon dioxide with alkylene oxide in the presence of a suitable catalyst. The disclosed catalyst is a tetraalkylphosphonium compound. This specification reveals that the catalyst used has been recycled. This specification further discloses that if the catalyst is recycled to the alkyl adipate in an alcohol (especially propylene glycol, 1,2-propanediol), the effectiveness of the catalyst is extremely stable.

A process for the preparation of alkylene carbonates is also disclosed in US-A 4,434,105. Reveal various catalysts. This document also describes that the catalyst can be reused after completion of the reaction.

In a continuous process, the reaction product containing an alkylene carbonate and a catalyst is treated. This treatment typically involves one or more distillation steps to separate the product from the catalyst. It has been found that if the catalyst is reused without taking appropriate steps to remove impurities from the catalyst to be recycled, the catalyst activity is reduced. These impurities include decomposition products of the catalyst. None of the above documents provide a means to avoid any accumulation of such impurities.

It has now been discovered that catalyst activity can be retained by purifying at least a portion of the catalyst from the product.

Accordingly, the present invention provides a process for producing alkyl carbonate by reacting an alkylene oxide with carbon dioxide in the presence of a rhodium catalyst, in which: (a) continuously introducing alkylene oxide, carbon dioxide and rhodium catalyst into the reaction zone a product stream comprising alkyl carbonate and a spent catalyst is withdrawn from the reaction zone; (b) separating the alkyl carbonate from the product stream and containing the spent catalyst; (c) recycling The product isolated alkyl ester of step (b); (d) purifying at least a portion of the stream containing spent catalyst to obtain a purified rhodium catalyst; and (e) purifying the rhodium catalyst Circulate to the reaction zone.

The method according to the invention allows the catalyst to be used for a long time in a continuous process. Factors have thus been found to be associated with the formation of decomposition products of the catalyst during the preparation of the alkyl carbonate. Impurities of the catalyst have been found to include phosphine oxide. By purifying the catalyst used, the phosphine oxide can be effectively removed so that the reactive catalyst can be recycled to the reaction zone in step (a). A further advantage of the method of the invention resides in the fact that the method preempts the necessity of including a effluent stream through which the contaminated catalyst must be withdrawn from the process.

The catalyst is a ruthenium compound. Such catalysts are known, for example, from US-A 5,153,333, US-A 2,994,705, US-A 4,434,105, WO-A 99/57108, EP-A 776,890, and WO-A 2005/003113. The catalyst is preferably a ruthenium halide of the formula R ₄ PHal wherein Hal means a halide and each R may be the same or different and may be selected from alkyl, alkenyl, cycloaliphatic or aromatic groups. The group R suitably contains from 1 to 12 carbon atoms. Excellent results were obtained in the case where R is a C _1-8 alkyl group. The group R is most preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl. The halide ion is preferably a bromide ion or an iodide ion. It appears that the bromine compound and the iodine compound are more stable than the corresponding chlorine compound. The best catalyst is tetrakis(n-butyl)phosphonium bromide. A further advantage of the process of the present invention is that it does not require expensive disposal of the effluent stream of the halogen containing catalyst. Purification of the used catalyst can be accomplished in a variety of ways. The catalyst used may be subjected to extraction, crystallization adsorption or other separation techniques. Preferably, the catalyst used is subjected to distillation.

It has been found that when the catalyst used is exposed to relatively high temperatures for a prolonged period of time, it tends to form decomposition products. Therefore, it is preferred to carry out the distillation at a relatively low temperature. The distillation method is suitably carried out below atmospheric pressure. The impurities in the catalyst composition are distilled by using a pressure below atmospheric pressure to leave a purified rhodium catalyst as a distillation residue. The distillation temperature is preferably not more than 250 °C. The distillation temperature is more preferably from 50 to 200 ° C, most preferably from 100 to 180 ° C. Suitable pressures for the distillation temperatures are from 0.1 to 0.0001 bar (10 to 0.01 kPa). The pressure range is preferably from 0.05 to 0.0005 bar (5,000 to 5 Pa).

Surprisingly, even when these distillation conditions were carried out, these rhodium catalysts completely recovered their activity.

Tantalum catalysts tend to be solid materials. The catalyst can be recycled to the reaction zone in solid form. It is also possible to convert the catalyst to a melt and recycle the molten catalyst to the reaction zone. However, since the presence of the solvent has a stabilizing effect on the catalyst, it is preferred to recycle the purified rhodium catalyst to the reaction zone in the presence of a solvent. The solvent may be a carbonyl containing compound, especially an aldehyde, as disclosed in WO-A 2005/051939. The solvent is preferably an alcohol. A wide variety of alcohols can be selected to increase the stability of the catalyst. The alcohol can be monovalent, divalent or multivalent. The alcohol may comprise an aliphatic C _1-12 chain substituted with one or more hydroxyl groups. An aromatic alcohol or an alkyl aromatic alcohol suitably having 6 to 12 carbon atoms can also be used. Polyalkylene glycols or their monoalkyl ethers can also be used. Mixtures can also be used.

The alcohol used is preferably selected from the group consisting of C _1-6 mono-alkanols, C _2-6 alkanediols, C _3-6 alkane polyols, including glycerol, phenols, C _1-6 alkyl groups. Substituted phenols, C _6-12 cycloaliphatic alcohols, and mixtures thereof. Very suitable are C _2-6 alkane polyols, especially 1,2-ethanediol, 1,2-propanediol, sorbitol and mixtures thereof. The use of ethane or propane diol has another advantage when converting alkylene carbonate to alkylene glycol (alkanediol) and the alkylene glycol is used as a solvent for the catalyst. Sorbitol provides excellent stability to the ruthenium catalyst. It may be advantageous to use 1,2-ethane or a combination of propane diol and sorbitol.

In order to supplement any decomposition catalyst, it is effective to add a recharge catalyst to the reaction zone. The replenishment catalyst can be added anywhere in the process where the catalyst is present. Any replenishing catalyst is added to the process as appropriate via direct addition to the reaction zone or via a stream of purified catalyst added to the recycle.

In the process of the present invention, at least a portion of the stream containing spent catalyst is subjected to a purification step. It is possible to carry out this purification for all streams and therefore all catalysts. However, it is preferred to carry out only partial purification. Thereby avoiding the accumulation of impurities. Furthermore, it has been shown that if the catalyst contains a small amount of such impurities, the impurities do not adversely affect the activity of the catalyst. It is clear that the fact that all catalysts must be continuously purified provides a significant economic advantage. Purification is suitably carried out with from 1 to 90% by weight, more preferably from 2% to 50% by weight, most preferably from 5 to 25% by weight of the stream containing the spent catalyst. Preferably, along with the purified rhodium catalyst, another portion of the spent catalyst-containing stream is recycled to the reaction zone. More preferably, the remainder of this stream is recycled to the reaction zone. Although it may not be necessary to vent the stream, a small amount of effluent stream may be applied.

The stream containing the spent catalyst suitably contains some alkylene carbonate. The alkylene carbonate ensures that the spent catalyst is in liquid form, which facilitates transportation, such as recycling. In addition, it has been found that the combination of an alcohol and an alkylene carbonate has a stabilizing effect on the catalyst. Therefore, if only partially used catalyst is used for purification, the alkylene carbonate is suitably combined to recycle the remainder of the catalyst used to the reaction zone. If the purified rhodium catalyst has been dissolved in the alcohol, the streams may be suitably combined such that the spent rhodium catalyst, the purified rhodium catalyst, the mixture of alcohol and alkylene carbonate are recycled to the reaction zone. If the alkylene carbonate is present in the stream containing the spent catalyst, the alkylene carbonate is separated from any phosphorus-containing impurities and catalyst during the purification step. This can be achieved in a distillation column where different fractions are obtained on different plates. However, it can also be carried out in two specific steps in which the alkylene carbonate is separated from the catalyst and any heavy chain impurities, and then the impurities are separated from the catalyst to obtain a purified rhodium catalyst. The latter approach has the advantage that optimal distillation conditions can be applied for each separation.

The alkylene oxide converted in the process of the invention is suitably a _C2-4 alkylene oxide, especially ethylene oxide or propylene oxide or a mixture thereof.

The amount of rhodium catalyst in the reaction zone can conveniently be represented by a molar catalyst/mole alkylene oxide. Due to the lower amount of by-products, the process is suitably carried out in the presence of at least 0.0001 moles of catalyst per mole of alkylene oxide. The amount of the catalyst is preferably in the range of 0.0001 to 0.1 moles of catalyst per mole of propylene oxide, more preferably 0.001 to 0.05 and most preferably 0.003 to 0.03 moles of catalyst.

The reaction of carbon dioxide with alkylene oxide is reversible. This means that the alkylene carbonate formed can be returned to carbon dioxide and alkylene oxide. The molar ratio between carbon dioxide and alkylene oxide can be as low as 0.5:1, more suitably from 0.75:1. In view of the reversibility of the reaction, it is preferred to ensure at least a slight excess of carbon dioxide, such as from 1.0:1 to 10:1, more preferably from 1.01:2:1, optimally from 1.01:1 to 1.2:1. A suitable method of establishing excess carbon dioxide is to carry out the reaction at high carbon dioxide pressure and maintain a constant pressure by giving carbon dioxide. The total pressure range is suitably from 5 to 200 bar; the partial carbon dioxide partial pressure is preferably in the range of from 5 to 70, more preferably from 7 to 50 and most preferably from 10 to 30 bar.

The reaction temperature can be selected from a wide range. The temperature is appropriately selected from 30 to 300 °C. The advantage of quite high temperatures is to increase the rate of reaction. However, if the reaction temperature is too high, side reactions may occur, that is, the alkylene carbonate is degraded to carbon dioxide and the improper reaction of propionaldehyde or acetone, alkylene oxide with any (possibly) alkanediol, or may accelerate the contact Improper decomposition of the media. Therefore, the temperature is suitably selected from 100 to 220 °C.

Those skilled in the art will be able to switch to other reaction conditions as appropriate. The residence time of the alkylene oxide and carbon dioxide in the reaction zone can be selected without undue burden. The residence time can generally vary from 5 minutes to 24 hours, preferably from 10 minutes to 10 hours. The conversion of the alkylene oxide is suitably at least 95%, more preferably at least 98%. The residence time can be adjusted depending on the temperature and pressure. The catalyst concentration can also vary over a wide range. Suitable concentrations, including the total reaction mixture, include from 1 to 25% by weight. Excellent results are obtained at a catalyst concentration of 2 to 8% by weight based on the total reaction mixture.

As for the relative amounts of alkyl carbonate and alcohol, those skilled in the art can vary the ratio over a wide range. Excellent results are obtained with a weight ratio of alkylene carbonate to alcohol of from 0.1 to 10, especially from 0.2 to 5, more preferably from 0.5 to 2. In view of the possibility of an improper reaction between the alkylene oxide and the alcohol in the reaction zone, the amount of the alcohol is suitably maintained at a relatively low level, such as from 1 to 25% by weight of the alkylene oxide, carbon dioxide, alkylene carbonate and the alcohol in the reaction zone. Wt. The amount of alcohol is preferably in the range of 5 to 20% by weight.

The alkylene carbonate produced by the method of the present invention can be suitably used for the production of an alkanediol and a dialkyl carbonate. Accordingly, the present invention also provides a process for the preparation of an alkanediol and a dialkyl carbonate comprising reacting an alkanol with an alkylene carbonate on a transesterification catalyst, wherein the alkylene carbonate has been prepared by the process of the invention And recovering the alkanediol and the dialkyl carbonate from the obtained reaction mixture. The alkanol is suitably a C _1-4 alcohol. The alkanol is preferably methanol, ethanol or isopropanol.

The transesterification reaction itself is known. In this case, reference is made to US-A 4,691,041, which discloses the use of an ion exchange resin in a heterogeneous catalyst system, especially a tertiary amine, a quaternary ammonium, a sulfonic acid and a carboxylic acid functional group, impregnated in a vermiculite. And a method for producing ethylene glycol and dimethyl carbonate by transesterification on an alkaline earth silicate and an ammonium ion exchange type zeolite. US-A 5,359,118 and US-A 5,231,212 disclose a continuous process for the preparation of dialkyl carbonates over a range of catalysts, including alkali metal compounds, especially alkali metal hydroxides or alcoholates, such as hydroxides. Sodium or sodium methoxide, hydrazine compounds, nitrogenous bases such as trialkylamines, phosphine, hydrogen halide, arsine, sulfur or selenium compounds and tin, titanium or zirconium salts. According to WO-A 2005/003113, the reaction of an alkylene carbonate with an alkanol is carried out on a heterogeneous catalyst such as alumina. In this document, it is proposed to remove the rhodium catalyst together with the alkanediol after the conversion of the alkylene carbonate to the alkanediol. However, it is preferred according to the invention to separate the alcohol (if present) at an early stage. In accordance with the present invention, it is preferred to separate the alcohol from the product stream comprising the alkylene carbonate and the spent catalyst. The amount of alcohol recycled in this manner can be kept to a minimum. In addition, any light halides that can be formed as by-products during the reaction are removed from the alkyl carbonate product and that it does not hinder any subsequent process steps. Preferably, the alkanediol is used as a solvent, and the purified rhodium catalyst is recycled to the reaction zone in the presence thereof, wherein carbon dioxide is reacted with the alkylene oxide to give an alkylene carbonate. In this way, the presence of foreign alcohol is avoided.

According to the above, the present invention further provides a process for producing alkyl carbonate by reacting an alkylene oxide with carbon dioxide in the presence of a ruthenium catalyst, in which: (a) continuous introduction of alkylene oxide, carbon dioxide and ruthenium catalyst In the reaction zone, a product stream comprising alkyl carbonate and a spent catalyst is withdrawn from the reaction zone; and (b) separating the alkyl carbonate from the product stream and the stream containing the spent catalyst. This separation can be suitably achieved via distillation. The alkylarsate product is typically recovered as overhead product after separation from the lighter alcohol, as appropriate. The bottom product contains spent catalyst and certain alkyl carbonates. A portion of this bottoms stream is then purified via a separate distillation section in accordance with the process of the present invention. The purified rhodium catalyst thus obtained is suitably dissolved in an alkanediol, and this solution is combined with the remainder of the stream containing the spent rhodium catalyst and alkylene carbonate. The obtained alkyl carbonate, alcohol, used ruthenium catalyst and purified rhodium catalyst are recycled to the reaction zone.

The invention will be further elucidated by means of the following examples.

Instance Example 1

To demonstrate the purification of the spent catalyst, the following experiments were performed.

The catalyst solution (100 ml) containing about 75% by weight of propylene carbonate and 25% by weight of the spent catalyst composition was distilled in a glass round bottom bottle. The catalyst composition used contained 18.2 mole% of tributylphosphine oxide and the remainder was tetrabutylphosphonium bromide. The first fraction was removed by distillation under vacuum at 65 ° C and 2 mbar (200 Pa). This fraction consists essentially of propyl carbonate. The residue was solidified by cooling and heated and melted again. The melt was subjected to distillation at 160 ° C and 1 mbar (100 Pa). A second fraction consisting essentially of tributylphosphine oxide is recovered. The residue remaining in the bottle solidifies and consists essentially of tetrabutylphosphonium bromide. The analysis showed that the residue contained 1.7 mol% of tributylphosphine oxide.

Example 2

To demonstrate the catalytic activity of the purified rhodium catalyst, two experiments were performed. In two experiments, 120 g of propylene oxide was introduced into a 1 liter autoclave. The autoclave was pressurized with CO ₂ and heated to 150 °C. The CO ₂ was introduced again until the pressure reached 20 bar. A solution of 250 mg of ruthenium bromide catalyst in 5 g of 1,2-propanediol was introduced into the autoclave. An additional 10 g of 1,2-propanediol was introduced. The pressure was kept constant at 20 bar by giving CO ₂ to the autoclave. After 5 hours, the introduction of CO _{2 was} stopped and the autoclave was cooled. The amount, conversion and selectivity of the propyl carbonate in the two experiments were determined.

The experiment was conducted in the same manner except that the catalyst was obtained from the residue of Example 1 in the case of Experiment 1, and in the case of Experiment 2, fresh high-purity tetrabutylphosphonium bromide (ex Fluka) was applied. These results are shown in the table below.

Claims (12)

A method for producing alkyl carbonate by reacting an alkylene oxide with carbon dioxide in the presence of a rhodium catalyst, in which: (a) the alkylene oxide, carbon dioxide and the rhodium catalyst are continuously introduced into the reaction zone, a product stream comprising alkyl carbonate and a spent catalyst is withdrawn from the reaction zone; (b) separating the alkyl carbonate from the product stream and containing the spent catalyst catalyst; (c) the step ( b) recovering the alkylene carbonate isolated as a product; (d) purifying at least a portion of the stream containing the used catalyst to obtain a purified catalyst, wherein the contained The purified portion of the catalyst stream is subjected to distillation at a temperature ranging from 50 to 200 ° C and a distillation pressure of from 0.1 to 0.0001 bar (10 to 0.01 kPa); and (e) recycling the purified rhodium catalyst to the reaction Area. The method of claim 1, wherein the catalyst is a phosphonium halide of the formula R ₄ PHal, wherein Hal means a halide and each R may be the same or different and may be selected from an alkyl group, an alkenyl group, a cycloaliphatic group or an aromatic group. group. The method of claim 2, wherein the catalyst is tetrakis(n-butyl)phosphonium bromide. The method of any of claims 1 to 3, wherein the distillation temperature is in the range of 100 to 180 °C. The method of any one of claims 1 to 3, wherein the purified rhodium catalyst is recycled to the reaction zone in the presence of a solvent. The method of any one of claims 1 to 3, wherein 1 to 90% by weight of the Purification is carried out with a stream containing spent catalyst. The method of claim 6 wherein 2 to 50% by weight of the stream containing the spent catalyst is purified. The method of claim 7, wherein 5 to 25% by weight of the stream containing the spent catalyst is purified. The method of any one of claims 1 to 3, wherein another portion of the stream containing spent catalyst is recycled to the reaction zone. The method of any one of claims 1 to 3, wherein a spent catalyst, a purified catalyst, a mixture of an alcohol and an alkylene carbonate are recycled to the reaction zone. A process for the preparation of an alkanediol and a dialkyl carbonate, which comprises reacting an alkylene oxide with carbon dioxide in the presence of a rhodium catalyst to produce an alkylene carbonate by the method of any one of claims 1 to 10, The alkanol is reacted with an alkylene carbonate on a transesterification catalyst, and the alkanediol and the dialkyl carbonate are recovered from the resulting reaction mixture. The method of claim 11, wherein the alkanediol is used as a solvent, and the purified rhodium catalyst is recycled to the reaction zone in the presence of the solvent.